The present invention relates to an illumination system capable of providing uniform illumination, and more particularly relates to an exposure apparatus incorporating the illumination system, and a semiconductor device manufacturing method using same.
Conventional exposure apparatus for manufacturing semiconductor devices include an illumination system for illuminating a circuit pattern formed on a mask and projecting this pattern through a projection optical system onto a photosensitive substrate (e.g., a wafer) coated with photosensitive material (e.g., photoresist). One type of projection optical system employs an off-axis field (e.g., an arcuate field) and projects and transfers only a portion of the mask circuit pattern onto the wafer if the exposure were static. An exemplary projection optical system having such a field comprises two reflecting mirrors, a concave mirror and a convex mirror. In such projection optical systems, transfer of the entire mask circuit pattern onto the wafer is performed dynamically by simultaneously scanning the mask and wafer in a fixed direction.
Scanning exposure has the advantage in that a high resolving power is obtained with a comparatively high throughput. In scanning-type exposure apparatus, an illumination system capable of uniformly illuminating with a fixed numerical aperture (NA) the entire arcuate field on the mask is highly desirable. Such an illumination system is disclosed in Japanese Patent Application Kokai No. Sho 60-232552. With reference to FIG. 1, an illumination system 10, disclosed therein, comprises, along an optical axis A, an ultrahigh-pressure mercury lamp 12, an elliptical mirror 14, and an optical integrator 16. With reference now also to FIG. 2, optical integrator 16 has an incident surface 16i, an exit surface 16e, and comprises a combination of four segmented cylindrical lenses 16a-16d. Lenses 16a and 16d are located at the respective ends of optical integrator 16, are oriented in the same direction, and have a focal length f1.
Lenses 16b and 16c are located between lenses 16a and 16d and are each oriented in the same direction, which is substantially perpendicular to the orientation of lenses 16a and 16d. 
Adjacent optical integrator 16 is a first condenser optical system 18 and a slit plate 20. With reference now also to FIG. 3, the latter includes an arcuate aperture 20A having a width 20W and a cord 20C. Adjacent slit plate 20 is a condenser optical system 22 and a mask 24.
Mercury lamp 12 generates a light beam 26 which is condensed by elliptical mirror 14 onto incident surface 16i of optical integrator 16. By virtue of having two different focal lengths, optical integrator 16 causes light beam 26, passing therethrough, to have different numerical apertures in orthogonal directions to the beam (e.g., in the plane and out of the plane of the paper, as viewed in FIG. 1). Light beam 26 is then condensed by condenser optical system 18 and illuminates slit plate 20 and arcuate aperture 20A. Light beam 26 then passes therethrough and is incident condenser optical system 22, which condenses the light beam to uniformly illuminate a portion of mask 24.
With continuing reference to FIG. 3, a rectangular-shaped re-ion 28 on slit plate 20 is illuminated so that at least arcuate aperture 20A is irradiated. Thus, light beam 26 is transformed from a rectangular cross-section beam to an arcuate illumination beam, corresponding to aperture 20A. Note that aperture 20A passes only a small part of the beam incident slit plate 20.
Generally, arcuate cord 20C is made long to increase the size of the exposure field on the wafer. In addition, arcuate slit width 20W is set comparatively narrow to correspond to the corrected region of the projection optical system used in combination with illumination system 10. The illumination efficiency is determined by the ratio of surface area of arcuate aperture 20A to rectangular-shaped region 28. This ratio is small for illumination system 10, an indication that the system is very inefficient, which is disadvantageous. As a result, the amount of light reaching mask 24 is fixed at a relatively low level. Since the time of exposure of mask 24 is inversely proportional to the amount of light (i.e., intensity) at the mask (i.e., the more intense the light, the shorter the exposure time), the scanning speed of the mask is limited. This limits the exposure apparatus"" ability to process an increasingly large number of wafers (e.g., to increase throughput).
The present invention relates to an illumination system capable of providing uniform illumination, and more particularly relates to an exposure apparatus incorporating the illumination system, and a semiconductor device manufacturing method using same.
Accordingly, the present invention has the goals of providing an illumination system capable of supporting higher throughput with an illumination efficiency markedly higher than heretofore obtained. Another goal is to maintain uniform illumination (e.g., uniform Kxc3x6hler illumination).
There has been a strong desire in recent years for a next-generation exposure apparatus capable of projecting and exposing a pattern having a much finer line width onto a photosensitive substrate by using a light source, such as a synchrotron, that supplies soft X-rays. However, prior art illumination systems are not capable of efficiently and uniformly illuminating a mask with X-ray wavelength light (xe2x80x9cX-raysxe2x80x9d).
Consequently, the present invention has the further goal of supplying an illumination system and exposure apparatus capable of efficiently and uniformly illuminating a mask with X-rays, and further to provide a method for manufacturing semiconductor devices using X-rays.
Accordingly, a first aspect of the invention is an illumination system for illuminating a surface over an illumination field having an arcuate shape. The system comprises a light source for providing a light beam and an optical integrator. The optical integrator includes a first reflective element group having an array of first optical elements each having an arcuate profile corresponding to the arcuate shape of the illumination field. Each first optical element also includes an eccentric reflecting surface comprising an off-axis section of a spherical reflecting surface or an off-axis section of an aspherical reflecting surface. The array of first optical elements is designed so as to form a plurality of arcuate light beams capable of forming multiple light source images. The illumination system further includes a condenser optical system designed so as to condense the plurality of arcuate light beams to illuminate the surface over the arcuate illumination field in an overlapping manner.
A second aspect of the invention is the illumination system as described above, wherein the condenser optical system comprises a condenser mirror with a focal point, with the condenser mirror arranged such that the focal point substantially coincides with the surface to be illuminated.
A third aspect of the invention is an illumination optical system as described above, further comprising a second reflective element group having a plurality of second optical elements. Each of the second optical elements has a rectangular shape and a predetermined second reflecting curved surface which is preferably an on-axis section of a spherical or aspherical reflective surface. The first and second reflecting element groups are opposingly arranged such that the multiple light source images are formed at the plurality of second optical elements when the light beam is incident the first reflecting element group.
A fourth aspect of the invention is an exposure apparatus for exposing the image of a mask onto a photosensitive substrate. The apparatus comprises the illumination system as described above, a mask stage capable of supporting the mask, and a substrate stage capable of supporting the photosensitive substrate. A projection optical system is arranged between the mask stage and the substrate stage, and is designed so as to project a predetermined pattern formed on the mask onto the photosensitive substrate over an arcuate image field corresponding to the arcuate illumination field.
A fifth aspect of the invention is an exposure apparatus as described above, and further including drive apparatus designed so as to synchronously move the mask stage and the wafer stage relative to the projection optical system.
A sixth aspect of the invention is the exposure apparatus as described above, wherein the illumination system includes a first variable aperture stop having a first variable diameter. The projection optical system further includes a second variable aperture stop having a second variable diameter. First and second drive systems are operatively connected to the first and second variable aperture stops, respectively, so as to change the first and second variable diameters, respectively. A control apparatus is also preferably included. The control apparatus is electrically connected to the first and second drive units so as to control the coherence factor by varying the first and second variable aperture diameters.
A seventh aspect of the invention is a method of patterning the surface of a photosensitive substrate with a pattern on a mask in the manufacturing of a semiconductor device. The method comprising the steps of first, providing an illumination light beam. The next (i.e., second) step is reflectively dividing the illumination light beam into a plurality of arcuate light beams corresponding to an arcuately shaped illumination field. The next step is condensing the arcuate light beams onto the mask over the arcuately shaped illumination field. The final step is projecting light from the mask onto the photosensitive substrate. The present method preferably further includes the steps in the above-mentioned second step, of first reflecting the light beam from a first array of reflecting elements each having an arcuate shape and a reflecting surface having an eccentric curvature, and forming a plurality of light source images, and then second, reflecting light from the plurality of light source images with a second array of reflecting elements opposingly arranged relative to the first array of reflecting elements.